Frequency Response Analysis for Quality Assurance Testing of Hairpin Stator Winding Insulation for Electric Vehicle Applications

With the rapid growth in electric vehicles (EV), hairpin wound stators are replacing random wound stators due to their higher power density and efficiency, and because of the ease with which manufacturing can be automated at a fast rate. Failure in the EV motor stator insulation is a major concern with increasing electrical stresses due to higher dc link voltage and wide bandgap devices. It is critical to implement a series of fast and effective quality assurance (QA) tests to screen defective units to maintain the quality and reliability, while keeping the production cost of EV motors low. Experience with EV motors showed that poor stator insulation quality is a leading cause of manufacturing defects in hairpin windings. In this work, the feasibility of applying frequency response analysis (FRA) for identifying defective hairpin stator insulation is evaluated. Test results on poorly impregnated EV motors with FRA and 6 common insulation tests show that FRA provides the most effective and reliable assessment of the insulation quality of hairpin wound stators.